1. Field of the Invention
The invention is directed to a new process for making hydroxy citric acid in a form that is stable and biologically active. Compositions containing the potassium hydroxy citric acid are useful as natural appetite suppressants.
2. Description of Related Art
During the 1970s, scientists at Brandeis University and at Hoffman LaRoche demonstrated that synthetic hydroxycitric acid, when blended with the diet, had a marked suppressive effect on weight gain in rats. The researchers noted that the HCA-treated rats tended to eat less; food consumption was suppressed by 10% or more on optimal HCA intakes, that is, when HCA constituted 1% or more of the diet.
The mechanism by which the HCA affected weight gain was not known. Since the brain uptake of HCA appeared to be negligible, scientists speculated that the appetite-suppressive effect of HCA was exerted not through central nervous system (CNS) action, but rather by directly affecting the metabolic processes of the organism.
One of the most metabolically active organs in the body is the liver. One important function of the liver is to insure that the blood maintains adequate concentrations of glucose to fuel the body""s energy requirements. The liver can store dietary glucose in the form of the polysaccharide glycogen, and release glucose when blood glucose levels are low. The liver can also synthesize glucose in a complex process known as gluconeogenesis, from either amino acids or lactic acid as starting material. This newly synthesized glucose can either be released into the blood stream to supply energy requirements of body tissues, or can be stored as glycogen for future use.
The direct parasympathetic connection between the liver and the CNS monitors the level of glucose and glycogen in the liver. A high level of glycogen, as a result of high glucose supply, is translated by the CNS as the state of satiety, which results in decreased craving for food.
Since increased glycogen in the liver aids satiety, the effect of HCA on gluconeogenesis in rat liver has been studied. It has been found that the rate of gluconeogenesis, from lactate or the amino acid alanine, was approximately doubled in HCA-treated rats. This result provides support for the idea that HCA causes the observed appetite suppression via altering the rate of gluconeogenesis.
However, it appears unlikely that reduction of food intake can entirely account for the substantial reductions in weight gain seen in HCA-treated rats. For example, in one study, the net reduction in food consumption during the 80 day study period amounted to only 4%xe2x80x94and yet the rats had gained 78% less weight than the controls over this period. Other studies, providing less dramatic results, suggested that the reduction of weight gain was disproportionately large compared to the reduction in food consumption.
Because of this discrepancy between considerable weight loss versus a meager appetite suppression, it has been postulated that HCA exerts a mechanism which increases fat burning, which in turn could decrease body weight, in addition to affecting gluconeogenesis.
Fat burning, or oxidation, plays a prominent role in liver metabolism. Liver metabolic activity accounts for over a quarter of the total body oxygen consumption in a subject at rest. The substantial energy needs of the liver are met largely by oxidation of fat. The dietary fat is absorbed by liver cells, which oxidize or burn it for energy in the mitochondria. The fats are transported from the cell cytoplasm into the liver mitochondria, by linking them to the special transporting molecule L-carnitine. This reaction is facilitated by the enzyme carnitine acyltransferase.
Carnitine acyltransferase is inhibited by malonyl CoA, which can be obtained from conversion of acetyl CoA. Malonyl CoA, can not only inhibit the fat burning process, but also increase the body fat synthesis, since it is the direct precursor for the synthesis of fat and cholesterol. The acetyl CoA is synthesized in mitochondria, but it has to be transported to the cell cytoplasm to exert its biochemical action. However, it cannot be transported to the cytoplasm from mitochondria before it is converted to citric acid. Thus, citric acid is a transportable form of acetyl CoA. Citric acid, once in the cytoplasm, is converted to acetyl CoA with the help of the enzymexe2x80x94citrate lyase. HCA was found to be an extremely potent competitive inhibitor of citrate lyase (Ki=0.15 xcexcM). The affinity of the enzyme for HCA was over a hundred times greater than the affinity of the enzyme for citric acid. This action was afforded only by a HCA in a pure acid form, but not in the lactone form.
The significance of citrate lyase inhibition by HCA is that without active citrate lyase, little acetyl CoA could reach the cytoplasm. This in turn would limit the availability of malonyl CoA and slow the synthesis of fats and cholesterol, while disinhibiting the metabolic breakdown of fat, or oxidation of fat.
In light of the considerations noted above, it is likely that the ability of HCA to promote fat loss in humans results primarily from the stimulation of fat oxidation.
Activation of fat oxidation in the liver also tends to stimulate gluconeogenesis, primarily due to increased activity of the key enzyme pyruvate carboxylase. This in turn may replenish the stores of liver glycogen, and send a message of satiety to the brain center.
The drawbacks of HCA use as a weight loss compound stem from the following problems:
1. The poor technology of HA extraction from the fruit of Garcinia cambogia often provides HCA in lactone form, which is inactive, or less active, in inhibiting the citrate lyase;
2. The HCA, if not stabilized chemically, has natural propensity to be converted to the lactone form in aqueous solutions and in the gastrointestinal tract, i.e., without absorption of HCA in pure acid form, the HCA can hot inhibit the citrate lyase; and
3. High concentrations of HCA, that is, 1% or more (by weight) of the daily dietary intake, are required to exert the metabolic activity, because of poor cellular uptake. Without absorption of HCA, and the presence of HCA in the cytoplasm in pure acid form, HCA can not inhibit citrate lyase and exert its inhibitory activity on acetyl CoA formation.
In the past, it has been difficult to isolate hydroxy citrate in a form which is both stable and biologically active. Hydroxy citric acid exists in two forms, the free acid form and the lactone form. The free acid form is biologically active and the lactone form is inactive. However, the free acid form is not stable and gets converted to its lactone form, which is stable but inactive.
One prior art isolation procedure, that of Y. S. Lewis et al., in Phytochem 1965, Vol. 4, pp. 610-625, results in the isolation of hydroxy citric acid lactone.
I. WATER EXTRACT OF (xe2x88x92) HYDROXYCITRIC ACID FROM FRUIT OF GARCINIA CAMBOGIA (Lewis, Y. S. and Neelakantan, S., phytochemistry (1965) Vol. 4; pp. 619-625)
The prior art procedure to obtain (xe2x88x92)HCA from Garcinia cambogia on a large scale included the following procedure:
1. The dried rind was cooked with about three volumes of water in an autoclave (10 lb/in2) for 15 minutes;
2. The resulting extract was filtered through a cloth and then through a paper filter;
3. The obtained filtrate was concentrated to a small volume, and the alcohol precipitation method removed pectin contamination;
4. The clear filtrate was then treated with potassium hydroxide (alkali) to form viscous, dark, heavy liquid; this treatment resulted in formation of a hygroscopic material consisting of potassium salt of hydroxycitric acid;
5. The clear supernatant was decanted off and the oily liquid washed with 60% alcohol several times;
6. By repeated treatment with absolute alcohol, the material could be dried to a pale yellow hygroscopic powder, which formed pure alkali salt;
7. Aqueous solutions of the alkali salt were passed through a cation-exchange resin (Zeocarb 215) for recovery of the acid;
8. The obtained (xe2x88x92)HCA was chemically unstable, and upon evaporation formed lactone.
Another process for isolation of lactone was reported by Y. S. Lewis.
II. ACETONE EXTRACT OF (xe2x88x92) HYDROXYCITRIC ACID FROM THE FRUIT OF GARCINIA CAMBOGIA (Lewis, Y. S. (1981) Methods in Enzymology, Vol. 77; Published by Academic Press; pp. 613-619).
1. One kg of fruit of Garcinia cambogia is kept in 1500 ml of acetone in an overnight;
2. The fruit is re-extracted in a similar manner;
3. Acetone is removed from the combined extracts by distillation;
4. The viscous residue is stirred with 1 liter of water at 45-50xc2x0 C.;
5. The mixture is filtered through cheesecloth;
6. The precipitated insoluble material is removed by filtration;
7. The reddish brown filtrate is treated with activated charcoal at 80-90xc2x0 C. and concentrated to a thick syrup;
8. The syrup is xe2x80x9cseededxe2x80x9d with a few crystals of the lactone and left overnight;
9. The yield is vigorously extracted with 3 liters of ether;
10. The combined extracts are dried over anhydrous sodium sulfate;
11. Ether is then removed, and the remaining material is white solid, consisting mainly of lactone. The yield is approximately 150 gm.
The principle of the present invention is to provide technology for extraction of HCA in pure acid form, and technology for chemical modification of HCA to afford chemically stable product, which will not convert into lactone form, which will not be hygroscopic, and which is soluble in aqueous solutions and easily absorbable by the gastrointestinal tract.
The invention provides HCA by combining it with potassium into potassium hydroxycitratexe2x80x94a water soluble salt. Potassium is an ion primarily found in the cell cytoplasm, and it can easily cross from outside the cell to inside the cell. The cell membrane permeability for potassium is 100 times higher than for sodium and 25 times higher than for chloride. Potassium salt of HCA acts as a transporter of HCA inside the cell, where the biochemical action of HCA is exerted.